New RAM Mysterious Problem: HELP!

ok, gave after 3 hours of testing. here's whats happening:
bought 2 of (kingston 2gb 1333mhz ddr3 non-ecc cl9 sodimm, standard 256m x 64 non-ecc 1333mhz 204-pin unbuffered) upgrade imac i3 late mid 2010.
infos: -i have lion installed
-i don't use kind of external hard drive
-i have nothing power cord connected
after installing, beautiful. lion running smooth. system 100% better 8gb.
tried print document ( have wireless hp photosmart d110a if matters ) , imac frozen , started make 3 beeps indicates ram problem. booted , in same printing process frozen again, beeps. then, took off 1 of modules, , wasn't able reproduce problem. opened lot of apps, used lot of ram, printed document, everything.
sure got bad module, decided try other one. surprise, couldn't reproduce freeze ! again tried 8gb, , while booting, frozen , beeped. changed modules positions , problem remained.
took off ram , tried 1 1 (only 2gb) 4 modules. , couldn't reproduce it.
tested modules rember , apple hardware test. ok.

so, going on? imac can't handle 8gb ? can't think of !
heeeelp me!!! have 7 days change new ram.
should take apple care?

edit:
running on 6gb apparently makes stable, no matter combination of modules use. prime95 can reproduce problem using 8gb. 6gb, fine. might logic board failing recognize 8gb ?

 

maybe have bad ram slot , happen leave same ram slot empty whenever have 3 modules installed.

 

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